While it is true that revenue ultimately wins the day, there is generally a strong correlation between ratings and revenue, particularly if you are talking about ratings in key demographics. There are mitigating factors. Ratings are much more important for agency and national sales where the product is more of a commodity sell. For retail, particularly those single station buys where an advertiser is sold on the concept of radio, it is easier to talk about the type of audience and the fit with their products. In those cases, an advertiser can make up for a lack of ratings sophistication by monitoring the cash register and seeing if the plan is working (as long as they give it enough time...).
Of course there are exceptions. MIKE-FM for instance, did stronger ratings than their revenue would lead one to believe. A big reason was that the jockless format made it difficult to sell personality endorsements, a significant drawback when competing Matty, Howie Carr, Loren and Wally, etc. "Oldies" had some inherent challenges. While I have not seen Boston ratings in quite some time, my guess is that is skewed to the older side of 25-54 and older. Additionally, I have spoken to a number of marketers who are reticent to link their product to something called "Oldies", hence the prevalence of "Classic Hits".